Wakeboard Release Mechanism

ABSTRACT

Wakeboarding causes a large number of knee injuries, especially to the ACL. These injuries occur from large tensile, compressive and rotational forces on the knees. Rotational and compressive forces cause meniscus tears. Rotation and tensional forces lead to ACL tears. Knee injuries may be prevented by releasing both feet from the board simultaneously at a force lower than the ultimate strength of the ligaments in the knee. This novel device releases both feet within 0.25 of a second at a force under 268 lbs.

The benefit of the Nov. 29, 2010 filing date of U.S. provisional patentapplication Ser. No. 61/417,530 is claimed under 35 U.S.C. §119(e) inthe United States, and is claimed under applicable treaties andconventions in all countries.

TECHNICAL FIELD

This invention pertains to a mechanism that will allow for thenear-simultaneous release of both feet from a wakeboard at a presetforce.

BACKGROUND ART

Wakeboarding is a sport similar to waterskiing in which riders arepulled behind a motorized boat. However, unlike waterskiing, theobjective of wakeboarding is to jump the wake produced by the boat andperform aerial maneuvers. Because riders become airborne, the sport isinherently more dangerous than waterskiing. Knee injuries, such asanterior cruciate ligament (ACL) tears, are common among wakeboarders,but there has not yet been a device aimed at reducing these injuries.

Wakeboards are mechanically simple devices. Because they lack movingparts, they can typically be used in excess of ten years. They areusually made of fiberglass, plastic, foam, or a combination of thesematerials. When foam is used, it is encased in layers of plastic orfiberglass so that it lasts a long time.

There are several aspects of the design of wakeboards that cause them tobe a hazard to the knees. The large surface area of the board causeshigh forces to be placed on the knees due to water resistance in theevent of a crash. During use, the board is perpendicular to the line ofmotion, which causes high lateral forces to be transmitted to the knees.Wakeboard bindings use stiffer materials than bindings for other watersports, which, while giving wakeboarders greater ankle support, alsocauses more stress to be transmitted to the knees, increasing thelikelihood of knee injury.

Current wakeboards use a design in which the bindings are rigidlyattached to the board. This design leads to two scenarios that oftencause knee injuries. First, if a rider's bindings are too tight and donot release in the event of a crash, the large tensile forces impartedon the knee are often enough to strain or even tear ligaments in theknee. Second, because a rider's feet are released from their bindingsindependently of one another, one foot can be released from its bindingbefore the other. If the rider is spinning when he/she hits the water,the rotation of the rider's body weight around the knee of the leg thatdid not release can cause severe knee injuries due to the largetorsional stresses imparted on that knee. The rider's front foot oftencomes out of its binding first, and the rotational inertia of therider's upper body causes high torsional stress to be placed on therider's back knee.

Most prior developments in the wakeboarding industry have been directedtowards increasing the performance of wakeboards. There have beenrelatively few innovations related to the safety of wakeboard design.Knee braces are an option available to wakeboarders, but they are costlyand usually only purchased after an initial injury to support acompromised knee. In addition, knee braces protect the knee frombuckling, but do not offer protection against tensile forces.

Comparing wakeboarding to the winter sport of snowboarding, snowboardingis less likely to result in knee injuries. This is because insnowboarding, both feet are attached to the board via ratcheting strapsthat virtually never release, unless something catastrophic occurs.Wakeboarding conditions appear to put wakeboarders at particular riskfor ACL injuries. There is an unfilled need for improved safety inwakeboard design.

There are four major ligaments of the knee: the anterior cruciateligament (ACL), the posterior cruciate ligament (PCL), the medialcollateral ligament (MCL), and the lateral collateral ligament (LCL).These ligaments constrain the motion of the knee and protect againstlarge tensile forces. The lateral meniscus and the medial meniscusprotect against compressive stresses.

The ACL limits forward movement of the tibia as well as rotation of theknee. Because both of these types of motion occur often in wakeboarding,the ACL is particularly susceptible to injury. The menisci absorbcompressive forces, such as the force from the femur pushing down on thetibia when landing on the water. The menisci are particularly vulnerablewhen there is rotation accompanied by a compressive force, as oftenhappens during landings.

A wakeboard in use can exert an upward force, pushing the rider's feetaway from the board. On a conventional wakeboard, the friction of a footin a boot exerts a downward force that keeps the foot on the board. Whenthe upward force is greater than the friction of a foot in the boot, thefoot is released. However, this is an imprecise method of release, andthe force required for release can vary greatly. Often, the force of thefriction of the boots is greater than the strength of the knee, whichcan lead to severe injuries.

Head injuries are also associated with wakeboarding. As the rider leavesthe wake produced by the boat, the rider lets the board extend behindthe rider's body, holds the position for as long as possible, and thentucks the board beneath the body before landing. However, if the riderdoes not pull the board underneath the body in time, the large surfacearea of the board causes it to act like a parachute when it dips beneaththe surface of the water, putting tremendous stress on the knees.Furthermore, because the board decelerates so rapidly while the rider'supper body continues to move forward at about 22-25 mph (a commonwakeboarding speed), the board can act as a pivot to slam the rider'shead into the water, which can cause a concussion.

DISCLOSURE OF THE INVENTION

We have discovered a novel wakeboard binding release mechanism thatallows for the near-simultaneous release of both feet from a wakeboardat a preset force. The novel mechanism improves the safety of awakeboard, and decreases the risk of both knee and head injuries.

A preferred embodiment is made from stainless steel, aluminum, andpolycarbonate components, which should last the lifetime of several setsof bindings.

Referring to the embodiment depicted in FIGS. 1 and 2, the bindings eachhave a plate 2 attached on the bottom. Each plate 2 has a dual bevelededge (upper and lower bevel) 4, 6. Two low-friction pins 8 (fixed to theboard) slide over the bevels 4 as the plate 2 is inserted.

In a preferred embodiment, the angle of the lower bevel 6 on the bindingplate 2 is greater than the angle of the upper bevel 4, so that theforce required to release the plate 2 is greater than the force requiredto put the plate back in place.

In the most preferred embodiment, a 45-degree incline is used on the topbevel 4 of the binding plate 2. This angle is large enough to push thespring to the side, but not so steep that the binding would release tooeasily. A 60-degree angle is used for the bottom bevel 6 of the bindingplate 2.

Also, in the most preferred embodiment, the plates 2 are narrower thanthose used in our initial prototype to protect against unexpectedrelease resulting from flexing of the plates.

FIG. 5 depicts the passive set-up of the device. The plates 2 are heldin position by springs 12, 14 that maintain force on the pins 8, 10, andthus on the bevel on the upper side 4 of the plate 2. One pin 10 is onthe outside and another on the inside 8 of each plate 2. The two pins 8on the insides of the two plates are coupled by a screw or shaft 16. Ina preferred embodiment, the length of the shaft 16 is adjustable. Thisadjustment is made, for example by a turnbuckle 18. Adjusting theturnbuckle 18 adjusts the amount of force exerted by the springs 12, 14on the pins 8, 10 and thus on the bevels 4 to keep the plates 2 inposition.

If the force imposed on one of the plates 2 exceeds the force holdingthat plate 2 in position (i.e., when the rider and the wakeboard move indifferent directions at sufficient velocity), then the plate 2 will bereleased, as shown in FIG. 6. The pins 8, 10 that hold the plate 2 inplace are displaced due to the force from the springs 12, 14. Becausethe inside pins 8 are coupled, when one inside pin 8 is displaced due tothe release of a plate 2, the force on the other inside pin 8 isreleased and the other plate 2 is also released, almost simultaneously,as shown in FIG. 7. The pins 8, 10 are preferably made frompolytetrafluoroethylene or from graphite composite.

A preferred embodiment uses four compression springs 12, 14 mounted inpolycarbonate blocks 20, 22 to accomplish the near-simultaneous releaseof the bindings, as shown in FIGS. 5-7.

There are at least four release mechanisms total, one on the inside andone on the outside of each of the two binding plates 2. The mechanismson the insides of the two binding plates 2 are coupled to each other,for example by a solid turn-buckle type arrangement 18, so that when onebinding plate 2 releases, a rod 16 instantly slides into the gap left bythe released binding plate 2 and the pressure is taken off of thecentral connection 16, which should be free to slide as a single unit.When this happens, pressure on the inside of the other binding plate 2is released, and the other binding plate 2 also releases. The outersprings 14 are used in case there is a torque on the binding plate 2that rotates the binding toward the center of the board, in which casethe outside of the binding plate 2 would lift and release first, andagain the other binding plate 2 would also be released.

A compression spring 12 is sandwiched between each shaft 16 and a boltwith a washer welded on the end to press against the spring 12. In apreferred embodiment, a square shaft and receiver combination is used onthe bolt to prevent rotation of the shafts 16 when the turnbuckle 18twists. The differences between the inner 20 and outer blocks 22 areshown in FIGS. 3 and 4.

In the prototype embodiment, the four blocks 20, 22 were manufacturedfrom polycarbonate. Its deformation under the maximum applied load wasin the order of 10⁻³ inches, which is an acceptable deformation based onthe results of a stress analysis.

A preferred embodiment employs both aluminum and stainless steel becauseboth are corrosion resistant. Stainless steel is preferred in higherstress areas where extra strength is needed, whereas aluminum ispreferred in lower stress areas to reduce the overall weight of themechanism. Both corrosion resistance and light weight are importantcharacteristics since the board is designed to perform airbornemaneuvers and because it spends time in and out of water. The mostpreferred embodiment uses springs with a corrosion resistant coating,such as zinc.

The invention should lead to a significant decrease in the number andseverity of not only knee injuries, but also head injuries sustainedwhile wakeboarding. Head injuries typically occur when the edge of theboard catches the water, causing the rider to slam face-first into thewater. However, with the novel release mechanism in place, the bindingsshould release as soon as the board dips beneath the surface, so thatthe rider maintains more forward momentum and is not slammed into thewater.

The same release mechanism disclosed here can also be used for quickrelease from a snowboard.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a prototype embodiment of the wakeboard releasemechanism.

FIG. 2 depicts a cross-section of the footplate and pin.

FIG. 3 depicts the outer release mechanism.

FIG. 4 depicts the inner release mechanism.

FIG. 5 depicts one embodiment of a complete device in accordance withthe present invention.

FIG. 6 depicts the initial stage of release of the first footplate fromthe mechanism.

FIG. 7 depicts the release of the second footplate.

MODES OF PRACTICING THE INVENTION

Noyes et al. The Journal of Bone and Joint Surgery. “BiomechanicalAnalysis of Human Ligament Grafts Used in Knee-Ligament Repairs andReconstructions.” 1984. reported measurements finding that the ACLstrength of 18 subjects with a mean age of 26 was 388±60 pounds. Basedon these measurements and assuming a normal distribution, a releasemechanism that imparts no more than 268 pounds of tensile force to theknees would be below the ultimate ACL strength of 97% of a 26 year-oldpopulation. Thus we chose 268 pounds as the maximum force for designpurposes.

The rider imparts a downward force upon the board through the boots, andthe board pushes up on the rider with the same force. The allowedmagnitude of this force is controlled by point at which the springsrelease the feet from the board. In a preferred embodiment, the bootsare held in place by 4 release mechanisms that function similarly tospring plungers. The stiffness of the spring controls the release force.In a preferred embodiment, a turnbuckle partially compresses the middlesprings, allowing for some adjustment of the spring stiffness, and thusadjustment of the release force.

The preset release force is less than about 1000 pounds, preferably lessthan about 500 pounds, and most preferably less than about 268 pounds.

FIG. 5 depicts one embodiment of a complete device in accordance withthe present invention. At the center is turnbuckle 18. Threaded throughturnbuckle 18 are two bars 16, each of which presses against a spring 12inside a hollow block 20. On the far end of each block 20 is a pin 8.Each pin 8 has a rounded end, which pushes down and holds a footplate 2in place. The footplates 2 each have a beveled edge, and are designed tohold the boots and feet of a rider. On the far side of each footplate 2is another hollow block 22, with a spring 14 and a peg 10, which help tostabilize the footplates 2.

FIG. 6 depicts shows the initial stage of release of left footplate 2for the same embodiment depicted in FIG. 5. An upward force, sufficientto overcome the preset spring force on the left pegs 8 and 10 that hadkept left footplate 2 in place, cause the left springs 12 and 14 tocompress into left block 18, and the left footplate 2 releases.

FIG. 7 depicts the subsequent release of right footplate 2. Once theleft footplate 2 has been released, there is no longer sufficient forceon turnbuckle 18 and on right springs 12 and 14 to hold the rightfootplate 2 in place, and right footplate 2 is thus released veryquickly.

Determining release force for a previous design wakeboard:

To determine the force required to release a rider's feet from thebindings of a previous design wakeboard, we used a Jackson StrengthEvaluation System. Tow straps anchored a load cell to an immobile, fixedstructure on one side and to the test wakeboard on the other side. Asecond tow strap near a subject's head was anchored to another immobile,fixed structure so that the subject could pull on the tow strap to applya force to the load cell. Before inserting his feet into the bindings,the subject wet his feet and the bindings to simulate the environment inwhich wakeboards are used. After inserting his feet into the bindingsand tightening them, he pulled as hard as he could on the tow strap, andthe results were recorded.

The maximum force applied during this test was 315 pounds, which was notenough to release either foot. It is uncertain how much greater theforce would need to release the subject's feet from the bindings. It isclear that the safety of wakeboards will be significantly improved witha release mechanism that requires a smaller force, such as 268 pounds orless, to release the rider from the binding.

Design Considerations

A maximum 268-pound limit for the release value was set. We consideredthis figure to be a conservative estimate for injury prevention based onthe average ACL strength of 388 pounds±60 pounds, as previouslydiscussed. Also, the other ligaments of the knee, such as the LCL andMCL, contribute to the overall tensile strength of the knee. The knee asa whole should withstand a greater force than an isolated ACL. Further,athletes such as wakeboarders are likely to have above-average ligamentstrength.

It is critical that the bindings for the two feet release virtuallysimultaneously, so that strong rotational force is never applied toeither knee. Adjustability of the minimum release force is an optionalbut preferred feature, so that beginners and advanced riders can use thesame device. Beginners will want the board to release more easily, whilemore advanced riders will want the board to be more difficult to releaseso that it doesn't release at inopportune moments, such as when therider is performing aerial maneuvers. A release force of 50-100 poundsis likely appropriate for a beginner, because beginners rarely becomeairborne. These beginner release estimates were determined throughexperiments in which we found that, so long as the bindings were lacedup, no matter how loosely, the feet did not pull out from the bindingswith a force less than 100 pounds. Fifty pounds was chosen as the lowerlimit to prevent the bindings from releasing accidentally due to wavesand small incidental forces that occur during normal wakeboarding. Asthe rider progresses, he or she will be able to increase the releaseforce of the bindings to suit ability.

Fabricating the prototype:

The first step in fabricating a prototype embodiment was to retrofit theoriginal bindings of an as-purchased wakeboard so that they werecompatible with the novel release mechanism. An aluminum diskapproximately one inch thick was machined so that the top and bottomedges had angles of 45 and 60 degrees, respectively. Next, five grooveswere cut into the top and bottom surfaces in each quadrant of the disk.A ⅛-inch deep rim was cut into the bottom surface of the disk to helpalign the individual pieces with the binding plate. Finally, threadswere tapped into the pieces, and they were attached to the board usingscrews. The heads of the screws, as well as the metal inserts in the topsurface of the board, were ground down for the bindings to fit flushwith the surface of the board.

The next step in the fabrication process was machining the polycarbonateblocks 20, 22. Several incremental cuts were made to create thenecessary holes in the polycarbonate blocks 20, 22.

A stainless steel turnbuckle 18 was manufactured, incorporating aone-inch diameter knob 24 so that adjustments could easily be made bythe end user, on the spot, without the use of tools.

Rods 16 for the central connection were fabricated from a 5/16-inchthick, square, stainless steel stock piece. One end of the rod wasrounded off, and threads were cut into the surface to interface with theturnbuckle 18. A washer was welded to the other end of the rod 16 topush against the springs 12. A receiver with a square hole was machinedfrom aluminum to accept the square section of the rod and preventrotation if the turnbuckle twisted. For the outer blocks 22, thereceivers had a circular, threaded hole in the center to enableadjustment by simply twisting the bolts. The individual components wereassembled using basic hardware such as bolts and washers, and themechanism was attached to the board using wood screws. The wholemechanism added about two pounds to the board, which weighs around 15pounds with bindings. The mechanism weighed less than 15% of the weightof the board.

Testing the prototype:

Four tests were performed on the prototype embodiment to determine thetime between release of the first binding plate 2 and the second bindingplate 2, and the force required to release the bindings.

For the speed test, a Sony Super Steady Shot HDR-SR11™ camera was usedin a high speed mode that recorded 120 frames per second. There were 5frames between the time when both binding plates were connected to theboard and the time when both binding plates were released, so the totalelapsed time was about 0.04 seconds.

We estimated that the maximum allowable release time to prevent injurywas probably between about 0.125 seconds and about 0.5 seconds. Theactual release time achieved with the prototype, about 0.04 seconds, wassubstantially faster. The invention allows the two bindings to releasenearly simultaneously, so that there is insufficient time for dangerouslevels of torsional force to be imparted to the knee due to rotation ofthe upper body around the knee.

To test the release force of the prototype, a Jackson-strengthevaluation system was used to measure the force exerted on the board bya test subject pulling his feet out of the bindings. The system wasconfigured to record only the peak force exerted on the load cell by thehuman test subject. In actual use, the strongest force should be thatjust before detachment, the force at which the binding releases from thewakeboard. A human test subject held a pair of handles and pulledhimself out of the bindings while lying on the ground. The force atwhich the bindings released from the board was recorded.

In the initial tests, four different preload settings were used on thesprings 12, 14, to vary the resistance to release. Eventually, we had tostop testing because the original turnbuckle 18, which was aluminum, wasbeginning to strip. The average values measured in tests at differentpreload settings were 178 pounds (n=19 releases), 118.7 pounds (n=10),162 pounds (n=8). Only two releases were recorded at the highest preloadsetting, 202 and 226 pounds, before the turnbuckle 18 stripped.

In a subsequent laboratory test, the release value was 182±6 pounds withover 15 releases tested. After the second lab test, the mechanism wastested on the water. In earlier tests, the mechanism released severaltimes when it should not have, when the binding plates 2 rotated out ofposition. Therefore, four pins were added (0.25 inch shoulderedstainless steel bolts) to the top of the board, using pre-existingthreaded inserts on the top surface. The pins fit into holes drilledinto the aluminum foot plates of the bindings, and helped inhibitrotation of the bindings. Springs with a spring rate of 508pounds-per-inch were used in the central connection 12, and springs witha spring rate of 165 pounds-per-inch were used in the outer blocks 14.When tested, the average release force was 222±22 pounds. One releaseoccurred at a force above 268 pounds, namely, 274 lbs, during thistrial.

In subsequent field tests following these design adjustments, the boardhad fewer accidental releases than in the first field test. In the latertests, the binding plates always released together, and the bindingplates were stable enough to permit jumping and even inverted aerialmaneuvers. The prototype binding plates 2 still released prematurely afew times, evidently due to flexing of the binding plate. To preventflexing and early release, the binding plate may be made substantiallynarrower, or it may be reinforced with a supporting material, or itcould be formed from a stronger material than that used in theprototype.

The complete disclosures of all references cited in this specificationare hereby incorporated by reference, including the complete disclosureof priority application No. 61/417,530. In the event of an otherwiseirreconcilable conflict, however, the present specification shallcontrol.

We claim:
 1. Apparatus for the rapid and essentially simultaneousrelease of both of a user's boots from a board, wherein the board is awakeboard or a snowboard; wherein said apparatus comprises: (a) twoboots and two plates, wherein said boots are adapted to receive theuser's feet, and wherein one of said plates is affixed to the bottom ofeach of said boots; (b) two pairs of receivers, one pair of saidreceivers associated with each of said two plates, wherein each of saidfour receivers is affixed to or is adapted to be affixed to the board;and wherein each of said pairs of receivers is adapted to receive and toengage one of said plates, and thereby to hold one of said boots inproximity to the board; (c) four pins, wherein one of said pins isassociated with each of said receivers; and (d) a coupler locateddirectly adjacent to two of said pins, wherein said coupler engages oris adapted to engage both of said adjacent pins, and to impose a forceon each of said adjacent pins; wherein the force upon either of saidadjacent pins is in a direction generally opposite to the direction ofthe other said adjacent pin, and wherein the force upon either of saidadjacent pins is in a direction generally toward the center of thecorresponding said plate; wherein: when in use, said coupler, pins,plates, and receivers cooperate and interact with one another asfollows: if only one plate is engaged with said plate's correspondingpair of receivers, then there is little or no force holding said platein proximity to the board, and said plate and said plate's correspondingboot may be removed from proximity to the board upon the application ofno force or a very small force; if both plates are engaged with thecorresponding pairs of receivers and pins, then both plates are held inproximity to the board by a substantial force, and said plates and bootsmay only be released from proximity to the board upon the application ofat least a threshold force to at least one of said boots or to at leastone of said plates; the threshold force is pre-determined or is set by auser; the threshold force is sufficiently high that the boots do notprematurely release during ordinary, non-injurious use of the board; andthe threshold force is sufficiently low that a boot will be releasedessentially simultaneously upon the application of a force to the bootthat could otherwise cause serious injury to a user's knee; and therelease of a first plate from the corresponding first pair of saidreceivers simultaneously releases the force that said first plate hadimposed upon the corresponding first adjacent said pin; and when theforce is released from the corresponding first adjacent said pin, theforce is also simultaneously released from said coupler and from thesecond adjacent said pin; and when the force is released from the secondadjacent said pin, the force holding the second boot and said secondplate to the board is simultaneously released, so that the second bootand said second plate are released from the board essentiallysimultaneously with the release of the first boot and the first saidplate from the board.
 2. Apparatus as in claim 1, wherein said couplercomprises a compression spring.
 3. Apparatus as in claim 1, wherein theboard is a wakeboard.
 4. Apparatus as in claim 1, wherein the board is asnowboard.
 5. Apparatus as in claim 1, wherein the threshold force isbetween about 50 pounds and about 300 pounds.
 6. Apparatus as in claim1, wherein the threshold force is between about 100 pounds and about 268pounds.
 7. Apparatus as in claim 1, wherein the threshold force isbetween about 268 pounds and about 500 pounds.
 8. Apparatus as in claim1, wherein the threshold force is between about 500 pounds and about1000 pounds.
 9. Apparatus as in claim 1, additionally comprising awakeboard, wherein each of said four receivers is affixed to saidwakeboard.
 10. Apparatus as in claim 1, additionally comprising asnowboard, wherein each of said four receivers is affixed to saidsnowboard.